Variable displacement pumps are commonly used in many different types of hydraulic systems. Some vehicles, such as, for example, work machines, commonly include hydraulic pumps that are driven by an engine or motor in the vehicle to generate a flow of pressurized fluid. The pressurized fluid may be used for any of a number of purposes during the operation of the vehicle. A work machine, for example, may use the pressurized fluid to propel the machine around a work site or to move a work implement on the work machine.
A variable displacement pump typically draws operating fluid, such as, for example, oil, from a reservoir and applies work to the fluid to increase the pressure of the fluid. The pump may include a pumping element, such as, for example, a series of pistons, that increase the pressure of the fluid. The pump may also include a variable angle swashplate that drives the pistons through a reciprocal motion to increase the pressure of the fluid.
A pump that includes a variable angle swashplate may also include a mechanism that varies the angle of the swashplate to change the stroke length of the pistons and thereby vary the displacement of the pump. The displacement of the pump may be decreased by changing the angle of the swashplate to shorten the stroke length of the pistons. Alternatively, the displacement of the pump may be increased by changing the angle of the swashplate to increase the stroke length of the pistons.
The amount of pressurized fluid required from a variable displacement pump may vary depending upon the particular operating conditions of the system or vehicle that relies upon the pump. In a vehicle application, the overall efficiency of the vehicle may be improved by varying the displacement of the pump to match the requirements of the vehicle. For example, if the vehicle requires less pressurized fluid, the angle of the swashplate may be changed to decrease the stroke length of the pistons. If the vehicle requires more pressurized fluid, the angle of the swashplate may be changed to increase the stroke length of the piston.
A vehicle or system may include a control system that monitors the operating requirements and controls the operation of the pump to match the requirements. To effectively match the output of the pump with the requirements of the vehicle or system, the control system monitors the current output of the pump by, for example, sensing the angle of the swashplate. If the control system can accurately determine the angle of the swashplate, the control system can accurately estimate the current output of the pump. The control system can then adjust the angle of the swashplate to match the requirements of the vehicle.
A variable displacement pump may include a sensor to monitor the angle of the swashplate. A swashplate sensor may be based on any of several different principles. For example, a swashplate sensor may be based on mechanical, light, electrical, or magnetic principles. However, the known sensors that are based on these principles are either unsuitable for use in a variable displacement pump or result in a significant increase in the overall cost in the pump.
For example, one type of swashplate angle sensor, manufactured by Rexroth, is based on a combination of electrical and magnetic principles known as the Hall effect. This sensor utilizes permanent magnets that are attached to the swashplate and extend outside the pump housing. A Hall-effect semiconductor chip is disposed between the permanent magnets. By directing a current through the semiconductor chip and measuring the resulting voltage across the chip, the angle of the swashplate may be determined. However, obtaining an effective seal between the pump housing and the member projecting outside the pump housing is difficult and expensive. In addition, any magnetic materials near the sensor may interfere with the operation of the sensor.
The sensor of the present invention solves one or more of the problems set forth above.